There is a need to provide particles with improved shatter resistance that can be used for a variety of applications. Specifically there is a need to provide products containing entrapped or encapsulated colorants, which products retain the colorant over extended periods and exhibit improved shatter resistance when subjected to different environments. This is particularly the case when employing oil soluble and water-soluble dyes, where it is generally difficult to permanently retain the dye. In a cosmetic composition if the dye is not permanently retained, this can impair the long-term visual effect of the cosmetic.
U.S. Pat. No. 5,234,711 describes a method for encapsulation of pigment particles utilized in ink formulations and their use for cosmetic products. The cosmetic products are especially directed to eyeliner pens.
U.S. Pat. No. 5,382,433 and published PCT Application WO 98/5002 describe the use of a cosmetic stick that contains microencapsulated pigment particles. The encapsulated pigment in the '433 patent is made by coacervation polymerization. The PCT application expands on this patent by including a volatile solvent in the cosmetic composition. The volatile solvent is present to minimize the gritty feel of the microencapsulated material.
A variety of techniques are known for providing encapsulated or entrapped colorants. For example, published PCT Application WO 91/06277 describes cosmetic formulations which have activatable dormant pigments dispersed in an anhydrous base or vehicle. A ground pigment or a liquid carrier dispersion is microencapsulated to form a stable, dry, free flowing powder of micro-sized particles. The preferred process of encapsulation is by coacervation, e.g. by emulsifying a liquid dispersion in a continuous, external aqueous phase to form micro-sized droplets and a complex of colloidal material is added to the external phase in such a way to form a deposit on or around each droplet thereby forming an outer wall or shell. The microcapsules are intended to rupture and release the dormant pigment when subjected to physical forces.
U.S. Pat. No. 5,234,711 concerns methods of encapsulating pigment particles useful in manufacturing of cosmetic products. It is an objective of this reference to employ an encapsulation process to increase the wettability, dispersibility and heat resistance of the pigment particles. The encapsulation method involves redox or free radical vinyl polymerization in an aqueous medium.
Published European Patent Application 225,799 describes a microencapsulated solid non-magnetic colorant material in a liquid, gel, wax or low temperature melting solid carrier phase, which is encapsulated within a polymeric shell. Absorbed onto the shell is a silane or titanate coupling agent, which increases the oleophilicity of the surface of the solid colorant material.
Published European Patent Application 445,342 relates to a cosmetic composition comprising a pigment that has been formed by incorporating a solvate dye into a resin and admixing with a cosmetic carrier. The amount of pigment present is sufficient to provide an attractive cosmetic effect when applied to skin, nails or hair. Any cosmetically acceptable soluble dye can be used. Any resin may be used provided it can be pulverized to a fine powder. The solvate dye may be incorporated into the resin by adding it to the elasticized or molten resin, or by dissolving the dye in a solution of unpolymerized resin and a mutual solvent for the dye and the resin, then polymerizing the resin, or by contacting the dye with the resin. The dye impregnated resin powders are said to be usable in a variety of cosmetic compositions.
WO 02/090445 addresses the problem of color retention and provides polymeric particles comprising a matrix polymer and colorant distributed throughout it. The matrix polymer is formed from a blend of monomers comprising a first monomer, which is an ethylenically unsaturated ionic monomer which is a salt of a volatile counterion and a second monomer, which is an ethylenically unsaturated hydrophobic monomer which is capable of forming a homopolymer of glass transition temperature in excess of 50° C. Typical matrix polymers include copolymers that have been formed from styrene with ammonium acrylate. The polymeric particles exhibit very good retention properties and are able to retain the colorant under an in a variety of conditions. However, these particles tend to suffer the drawback that they can fracture and even shatter under certain conditions when handled harshly, and this can lead to loss of the colorant.
Copending U.S. patent application Ser. No. 10/785, 208 describes the use of a blend of microencapsulated colorants prepared as described in WO 02/090445 in cosmetic compositions. The blend produces a textured natural tone coloring when applied, or creates similar effects on or in the cosmetic product itself. However, as noted above, the microcapsules are structurally different from those employed according to the present invention and lack their shatter-resistance.
An objective of the present invention is to provide cosmetic compositions comprising polymeric particles containing entrapped or encapsulated colorants, which compositions retain the colorant over extended periods and also when subjected to different environments. This is especially important when the colorants are oil-soluble and particularly water-soluble dyes, where it is generally difficult to permanently retain the dye. In a cosmetic composition, if the dye is not permanently retained, this can impair the visual effect of the cosmetic after prolonged use.
Encapsulation or entrapment of colorants can result in visual impairment of the colorant. This may be as a result of the polymer absorbing light from certain wavelengths or sometimes as a result of the irregular morphology of the polymer particles. This is also true where the particles are not shatter resistant. Fractures in the particles or broken particles will also lead to visual impairment of the colorant.
Thus another objective of the present invention is to provide cosmetic compositions comprising polymer-entrapped colorants in which the particles are shatter resistant and can withstand harsh handling, thus providing improved visual effects.